Groundwater in Little Lake Valley

Detailed federal and state studies from the 1960s and 1980s determined Little Lake Valley had a substantial and mostly untapped water aquifer available for domestic, agricultural, municipal and industrial use, containing on the order of 35,000 to 91,000 acre feet of water. In 2012, Brooktrails and Willits water plants combined produced a total of 1,209 acre-feet of water.

The 1986 study conducted by the U.S. Geological Survey, the California Department of Water Resources and Mendocino County determined an estimated 35,000 acre feet of water was stored in underground geological strata which could support wells suitable for municipal use. This study also looked at water quality, established likely locations for effective municipal wells and estimated the probable volume available for use by the city. They concluded that although there were areas of higher concentrations of heavy metals, such as boron, manganese and arsenic, that could restrict the use of wells in some locations within the valley for certain uses, there was plenty of water to support the needs of the Little Lake Valley at that time and into the foreseeable future.

Treating drinking water to remove heavy metals in the concentrations found in Little Lake Valley is well understood with off-the-shelf technology. Many places in the U.S. and in the world already treat water that has more contaminants than found in the Little Lake Valley.

It is also clear that many local residents are concerned with how effectively these contaminants can be removed. Arsenic is a particular concern to many residents. The city's park well produces water with more than 10 times the current Environmental Protection Agency allowable concentration for drinking water.

The Willits city staff has stated the intent is to reduce the arsenic levels down to two parts per trillion. This is the level observed in water in the city reservoirs.

Even the EPA limit of 10 parts per trillion is considered too high by many. In 2004 the California Office of Environmental Health Hazard Assessment recommended the maximum be lowered to four parts per trillion based on data from population studies in Taiwan, Chile and Argentina. This recommendation was not adopted by the California Department of Health because of the expense. The costs to reduce the arsenic in all California water supplies down to 8 parts per trillion would increase water treatment costs statewide by 50 percent. To drop the concentration to the two parts per trillion being proposed by the City of Willits would increase costs by six-fold, according to a California Department of Public Health in its statement of reasons for setting the arsenic maximums at the EPA limit.

Assuming the removal of the heavy metals and any other contaminants, the residential impact of displacing reservoir water with well water for part of the year would still be significant due to the hardness of the well water.

Willits is one of the few municipalities which has not used well water for of its water supply. Ukiah, Talmage, Cloverdale, Laytonville, Guerneville, Geyserville and others had wells being used for public water supplies according to the 1965 U.S. Geological Survey groundwater assessment of Russian River Valleys plus Round, Laytonville and Little Lake Valley.